Certain chemical vapor deposition processes, particularly those associated with large scale fabrication of epitaxial semiconductor devices, produce highly toxic effluent gases, such as dichlorosilane, trichlorosilane, phosphene, arsine, and hydrogen and nitrogen derivatives which have been changed within the fabrication reactor. These toxic gaseous effluents are typically heavily laden with e.g. silica particles which must be removed before the gases may be further processed, diluted and/or neutralized prior to discharge into the ambient envrionment. Other water soluble components present in the effluent include hydrochloric acid and residuals of phosphene and arsine.
Because of the high content of particulate components of the gaseous effluent, one significant drawback of prior art scrubbers is the susceptibility thereof to inlet plug-up and accumulation of clumps or masses of particulate matter. By "plug-up" herein is meant the formation of reaction residues when silicon-based gases come into contact with moisture. The reaction residues typically become formed and accumulate at the inlet of the scrubbing apparatus and plug it up.
Other portions and areas of the prior art scrubber have typically accumulated the clumps or masses of particulate matter and have required periodic cleanout. The buildup of massive particulate accumulations and residues not only diminishes scrubbing effectiveness, it also creates an explosion hazard. Clumps of residue which break off may result in a static electricity discharge sufficient to cause a spark and a resultant explosion in the hydrogen-rich environment. Also, larger pieces of residue and buildup may cause serious damage to and excessive wear in recirculation pumps which recirculate the scrubbing liquid throughout the scrubber process.
The prior art scrubbers have therefore typically required very frequent inlet plungings and periodic interior cleanings, usually carried out manually, in order to remove the deposited effluent costituents and prevent residue buildup with its concomitant explosion hazard. Not only are manual cleanings labor intensive, they may expose the operator to the toxic materials and require extensive precautions for operator safety, not to mention down-time of the scrubbing process itself. Prior art scrubbers typically require inlet plunging about twice per day, or even more frequently, depending upon the level of particulates present in the gaseous effluent stream and the rate of buildup at the input.
Once the gaseous effluent is drawn into the scrubbing apparatus, conventional scrubbing techniques may thereupon be applied to scrub the gas, i.e. dissolve the soluble components and wet and thereby remove the silica particulates. Typically, such prior techniques have included static water spray followed by passage of the effluent/scrubbing liquid through a filter medium. The filter medium is typically arranged to present maximum possible obstruction in wetted areas of the scrubber for a given distance travelled by the scrubbing liquid. One drawback of static water spray techniques is the tendency of the static spray to cause channels and tunnels to form through the filter media with concomitant loss in scrubbing efficiency.
Thus, a hitherto unsolved need has arisen for a fume scrubber which may be constructed from readily available, standard components and materials, which effectively draws a particulate-laden gaseous effluent stream into the scrubber without accumulation and blockage over time, and which effectively and efficiently scrubs the particles and solubles from the effluent stream in a continuous process without buildup of any residues or deposits and with very modest consumption of scrubbing liquid.